In an image forming apparatus utilizing electrophotographic method, an electrostatic latent image is formed on a photosensitive member and is developed by a developing device to form a toner image, which is first transferred to an intermediate transfer body and then transferred second and fixed to a recording medium such as paper. When performing full-color printing with such image forming apparatus, four toners of yellow, magenta, cyan and black are used. The toner images are first transferred to and superposed on an intermediate transfer body by a four-cycle system or a four-tandem system, and then secondly transferred and fixed to a recording medium (refer to the patent document 1-3, for example).
In the four-cycle method, toner images of yellow, magenta, cyan and black are successively formed on one photosensitive member, and then first image transfers of the toner images to an intermediate transfer body are successively performed. Meanwhile, in the four-tandem method, a plurality of photosensitive members are prepared for forming each of the toner images on a respective one of the photosensitive members, and first image transfers of the toner images to an intermediate transfer body are successively performed.
However, in the image forming apparatuses utilizing such systems, even after transferring the toner images of the photosensitive members, the toners partly remain on the photosensitive member. The residual toner may be removed by a cleaning device, still, it is difficult to completely remove the toner. When image forming is performed using a photosensitive member with unduly remaining toner, flaws of black spots or image deletion may be caused. Especially when using the image forming apparatus repeatedly, fusion of the residual toner may occur, thereby constantly causing flaws in images.
Further, by repeatedly using the image forming apparatus, the surface condition (surface free energy) of the photosensitive member may be changed, and thus the adherence (work of adhesion) between the toner and the photosensitive member is changed. As a result, quality of the toner image transferred from the photosensitive member to the intermediate transfer body may get deteriorated with use of the image forming apparatus, so that flaws in images are likely to be caused.
Flaws in images largely affect the duration of guarantee of an image forming apparatus for forming images of a constant quality. Especially, when performing full-color printing, it is required to have an image property higher than when performing black-and-white printing. Thus, the image forming apparatus for full-color printing is highly required to prevent flaws in images for a long period.
Patent Document 1: JP-A-2006-162951
Patent Document 2: JP-A-2004-233914
Patent Document 3: JP-A-9-152791